The invention relates to a system for the reliable prevention of the restarting of a machine.
For the protection of persons who work on equipment and machines or maintain them particular measures must be provided. There are various legal provisions which lay down the conditions for reliability functions. Widely disseminated is the use of repair switches which are intended to make individual parts of the machine or equipment power-free. However, these show failures even after 20,000 to 50,000 switching cycles and thus represent a potential risk.
In the case of production machines of larger dimensions the repair switches are disposed at points widely separated from one another. This leads to additional problems in monitoring since it cannot be insured that the component to be maintained is actually free of power. Motions causing danger must however be ruled out in the machine.
It is the objective of the invention to provide for a system which reliably prevents the restarting of a machine and which also can be used in spatially extended equipment.
This objective is realized by a system according to claim 1. Preferred embodiments are subject matter of the subclaims.
These are provided according to the invention, at least one disconnect switch which is disposed at the site of the machine at which the machine power is to be switched off, where each disconnect switch issues a disconnect signal to switch off the machine power, a power supply unit connected between the main switch of the main power circuit and the machine, where the main switch is at the power supply input of the power supply unit, and its power output is connected to the machine which maintains the supply of power to the machine interrupted by means of a power connection apparatus if at least one disconnect switch issues a disconnect signal, where a power monitoring apparatus checks the power output of the power supply unit for a voltage-free status, and the power connections apparatus which only permits a restart of the machine when none of the disconnect switches are issuing a disconnect signal; a control unit with a predetermined number of inputs for disconnect switches, or, if necessary, a collection and distribution unit, either of which reports the presence of a disconnect signal at one of its inputs to the power supply unit and receives the status of the power monitoring apparatus of the power supply unit and when the power-free status is reported issues a verification message to the disconnect switch which has supplied the disconnect signal; and, in case the number of disconnect switches is greater than the number of inputs of the control unit, at least one collection and distribution unit which has a predetermined number of inputs for disconnect switches or for an additional collection and distribution unit where at its output a disconnect signal is issued when a disconnect signal is present at one or more inputs.
The system according to the invention is used in particular for the prevention of an unexpected restart of the machine in whose main power circuit it is installed. Therein the power-free status of the power supply output of the system is verified visually. The system is configured so that it is flexible, thus being able to be used in the most various types or sizes of machines. Technical aspects and safety aspects were taken into account therein so that the installation can be carried out in practically every country in the world.
The system according to the present invention is not intended to switch off the system under load, it is not intended to be used as an Emergency Off switch, and it is not intended to be in the position by itself to permit the machine to start up. It is also not intended to replace a main switch. The machine must have its own Start/Stop commands so that an automatic Start is ruled out if the system according to the invention shows power at the power supply output. The system described in this invention, however, will not allow reclosure of the power connection apparatus if a fault is detected until the fault is cleared.
It is possible that individual machine components continue to be excluded from this safety system. This can relate, for example, to heating devices for adhesives and the like whose switching off may destroy parts of its equipment.
In principle forming the power supply unit and the control unit as an integrated component could be provided but as a rule they will be separate components.
The switch-off system of the invention thus comprises four different modules:
disconnect switches which offer the possibility to the operators of safely switching off the electrical power from the machine before they begin their work in a dangerous environment. These switches issue a disconnect signal and receive the (preferably visually displayed) verification of the power-free status,
collection and distribution units that collect and concentrate information from the disconnect switches or additional collection and distribution units. For this purpose a unit of this type preferably has a safety device with expansion modules for the transmission of the disconnect signals. The collection and distribution units also transmit the verification signal to the disconnect switch which has issued the disconnect signal.
a control unit which is used as the interface between the power supply unit and the collection and distribution units as well as to the disconnect switches. It is also responsible for the supply of power to the collection and distribution units and the verification message and includes the functionality of a collection and distribution unit. Preferably a monitoring relay, which receives the message concerning the status of the power monitoring apparatus of the power supply unit PB, as well as having a safety circuit which transmits the verification message concerning the power-free status of the power monitoring apparatus to the disconnect switches DS, is provided, more preferably a stabilized DC power source for the monitoring relay, the safety device in the control unit and for the safety device in the collection and distribution units, a non-stabilized DC power source for the verification circuit, and an insulation monitoring circuit for monitoring the insulation between lines which are held at the potential of the stabilized DC power source and lines which are held at the potential of the non-stabilized DC power source,
a power supply unit which transmits or disconnects the power for the machine or equipment though the power connection apparatus, a power monitoring apparatus, a control power supply source and, more preferably, a xe2x80x9cfour-relayxe2x80x9d safety circuit.
The control unit as well as the collection and distribution units are the same for all forms of embodiment of the system according to the invention in whatever machine or equipment they are used. The monitoring is done practically independently of the size of the machine since the main circuits only run in the power supply unit.
The minimal configuration of a system according to the invention includes the power supply unit, the control unit, and as well as at least one disconnect switch. The maximal configuration will depend on the number of disconnect switches required as well as on the distance of each collection and distribution unit as well as of each disconnect switch from the control unit.
In normal operation all disconnect switches are closed, that is, none of them issues a disconnect signal. Now if it is intended to provide for a reliable switch-off, the machine must first be stopped. This can, for example, happen through the agency of software by which a stop command is used by the machine. The operator who must work in an area will then switch the corresponding disconnect switch and lock it in the open position. Thereby a disconnect signal is issued which is provided to the power supply unit. On occurrence of the signal it will be checked according to set criteria whether the output of the power supply unit is power-free. When and only when this power-free status is actively confirmed will a verification display on the disconnect switch which has the disconnect signal light up and verify the power-free status. Only then may operators enter into the corresponding area of the machine. As soon as they have finished their work, they will unlock the disconnect switch and once again turn on the equipment. The verification display shuts itself off.
If all the disconnect switches are switched on, the supply of power to the machine is restored and it can be restarted via the Start command.